A Class-D amplifier has very high efficiency, and is often used to amplify an audio signal in a portable communication device having a speaker. High speaker output volume in a portable communication device is generally desirable; however, providing higher volume requires a power supply voltage that often exceeds the maximum voltage of modern power sources. For example, a lithium-ion battery typically is limited to a five (5) volt (V) maximum voltage output, while a class-D amplifier used to provide an audio signal to a speaker generally requires a voltage that exceeds 5V, particularly at higher volume output levels. To accommodate the higher voltage output, a boost circuit can be coupled to the Class-D amplifier and can be configured to raise the supply voltage above 5V to power the class-D amplifier to provide higher volume output levels. At lower volume output levels, the boost circuit may operate in what is referred to as a “bypass mode”, thereby preserving the efficiency of the class-D amplifier. At higher power levels, the boost circuit can provide additional supply voltage to the class-D amplifier so that the class-D amplifier may provide higher speaker volume. However, at higher levels of supply voltage, the efficiency of the combination of the boost circuit and the class-D amplifier typically degrades, particularly as power levels increase and the class-D amplifier spends less time in bypass mode. Therefore, it would be desirable to have a boost circuit and class-D amplifier that allows periodic higher volume output and that maintains the efficiency of the class-D amplifier over a wide range of power output levels.